A variety of face masks is known in the art and found in the market place, including re-usable and disposable masks, face masks for medical use, typically by surgeons, face masks for professional use where the inhaled air in the working environment requires so, and face masks for private use, e.g. for the prevention of spreading of infections, which are most widely used in Asian countries.
Prior art in the field of face masks includes the following documents:
U.S. Pat. No. 4,966,140, issued on Oct. 30, 1999, which discloses a face mask for the protection of the operating surgeon. The face mask comprising substantially vertical fasting tapes and a sealing strip formed along the upper marginal portion.
U.S. Pat. No. 5,735,270, issued Apr. 7, 1998, which discloses a disposable, foldable face mask comprises a single generally rectangular sheet of filter material, a foam sealing strip and a mask tieing device attached to the top corners.
U.S. Pat. No. 5,724,964, issued Mar. 10, 1998, discloses disposable face masks to be secured by a knitted head band to the head of the wearer which employs various gasket-type sealing material such as plastic film and/or hydrogels or other types of deformable material such as open cell and closed cell foams. Notably, adhesive types of hydrogels are not contemplated in this invention.
JP 10-248,948, filed Mar. 11, 1997, discloses a face mask to cover the nose and the mouth which comprises an adhesive material at the periphery of the face mask.
WO 00/07636, filed on Jul. 30, 1999, discloses novel hydrogel adhesives particularly suitable for disposable absorbent articles but also useful for respiratory face masks.
U.S. Pat. No. 4,240,420, issued on Dec. 23, 1980, and its continuation-in-part U.S. Pat. No. 4,354,4889, issued on Oct. 19, 1982, disclose filter masks which comprise separate filter elements for the nose and for the mouth of the wearer.
The prior art in the general field of adhesives for attachment to the skin is particularly developed in the field of articles such as band-aids, plasters and bandages.
In order to provide the desired level of adhesion of such bandages, the prior art typically discloses the utilisation of certain adhesives having very high cohesive strengths such as rubber based adhesives and acrylics. These adhesives are then applied as thick layers to maximise the adhesive force by which the bandage is secured to the skin of the wearer.
U.S. Pat. No. 4,699,146 discloses hydrophilic elastomeric pressure sensitive adhesives suitable for use with ostomy devices, bandages, ulcer pads, sanitary napkins, diapers, and athletic padding. The adhesive comprises at least one radiation cross linked organic polymer and an adhesive plasticiser.
GB 2 115 431 discloses adhesives for bandages, wounds or burn dressings, EKG adhesives, sanitary napkins, diapers and ulcer pads. The adhesive comprises an irradiation cross linked organic polymer such as polyvinylpyrrolodine and an adhesive plasticiser.
However, for satisfactory use with a device such as a respiratory face mask, which may be worn over extended periods of time, it is important that the adhesive has a skin compatible composition and not be harsh or aggressive towards the skin or cause skin irritation or inflammation. Also it is preferred if the adhesive is compliant with the skin of the wearer such that maximum skin surface contact between the adhesive and the skin is achieved. Moreover, it is also desirable to provide an adhesive such that the respiratory face mask can be readily removed from the wearer, without the wearer experiencing any unacceptable pain level and without leaving residues. This is particularly important under circumstances, where the device is removed and reapplication of the device once or even a number of times is required for example to allow for better communication, eating or the like, and to ensure the application of such devices on sensitive skin, e.g. of an elderly wearer. However, on the other hand the desired level of adhesion, albeit painless should of course also be maintained during such multiple applications of the device.
The problem of achieving the desired adhesion level is further exacerbated under wet skin conditions. In some cases, prior to the placement of the device the skin is cleaned and is usually as a result moist. Moreover, moisture from sweat may be developed while wearing a face mask, for example due to high ambient temperature or heavy physical work. The currently available adhesives, such as those containing hydrocolloid particles, however often do not immediately strongly adhere to the skin and may need to be held in place until sufficient minimum adhesion occurs. Moreover, the overall adhesive ability of such adhesives tends to be significantly reduced on wet skin surfaces per se, so that the device will typically not remain attached to the skin during wear if any pressure is exerted onto the device, for example by facial movements.
Another problem which is particularly prevalent for respiratory face masks usage is the ability of the adhesive to adhere on greasy or oily skin surfaces. The levels and types of grease and sebum naturally present on the skin vary from person to person. Further, the adhesive should reliably stick to hair populated skin and allow for painless removal even therefrom.
For example, WO-A-97/24149 (3M) describes a lipophilic polar pressure sensitive adhesive stated to have enhanced adhesion to greasy skin, the adhesive including a hydrophilic polymer matrix, a polar organic plasticiser and at least 9 wt % of a surfactant having an HLB (hydrophile lipophile balance) value of 10 to 17. It is stated generally that the hydrophilic polymer matrix may be selected from a range of polymers including homo- and copolymers of, for example, (meth)acrylic acid and salts thereof, acrylamide, N-vinyl pyrrolidone and acrylamidopropane sulphonic acid and salts thereof. The adhesive is prepared by polymerisation in a homogeneous aqueous mixture.
In view of the prior art mentioned above there still exists a need to provide an improved respiratory face mask, which meets the following objectives:                The mask is comfortable and safe to wear.        The mask is cheap to manufacture, so that it can serve as a disposable article, however, may alternatively be reusable many times.        The mask allows for facial movement, namely to at least somewhat open the mouth, to speak, to cough and the like, while maintaining a reliable sealing to the face.        The mask can be provided in one size to fit a large variety of consumers.        The mask works well on wet, greasy and in particular hair populated skin.        The mask reliably adheres to human skin over extended periods of time.        The mask can be easily and comfortably removed.        
It is another objective of the present invention to provide a cover layer for an adhesive layer, as preferably comprised by the face mask, the cover layer being easy to peel off from the adhesive and facilitating the optimal application of the mask to the face of a wearer.
It has now been surprisingly found that the above objectives can be meet by providing a respiratory face mask and a cover layer for an adhesive layer on the face mask both with the mechanical properties as defined hereinafter and preferably comprising an adhesive as defined hereinafter.